Interleukin 23 (IL-23), a heterodimeric cytokine, is a potent inducer of pro-inflammatory cytokines. IL-23 is related to the heterodimeric cytokine Interleukin 12 (IL-12) both sharing a common p40 subunit. In IL-23, a unique p19 subunit is covalently bound to the p40 subunit. In IL-12, the unique subunit is p35 (Oppmann et al., Immunity, 2000, 13: 713-715). The IL-23 heterodimeric protein is secreted. Like IL-12, IL-23 is expressed by antigen presenting cells (such as dendritic cells and macrophages) in response to activation stimuli such as CD40 ligation, Toll-like receptor agonists and pathogens. IL-23 binds a heterodimeric receptor comprising an IL-12Rβ1 subunit (which is shared with the IL-12 receptor) and a unique receptor subunit, IL-23R. The IL-12 receptor consists of IL-12Rβ1 and IL-12Rβ2. IL-23 binds its heterodimeric receptor and signals through JAK2 and Tyk2 to activate STAT1, 3, 4 and 5 (Parham et al., J. Immunol. 2002, 168:5699-708). The subunits of the receptor are predominantly co-expressed on activated or memory T cells and natural killer cells and also at lower levels on dendritic cells, monocytes, macrophages, microglia, keratinocytes and synovial fibroblasts. IL-23 and IL-12 act on different T cell subsets and play substantially different roles in vivo.
IL-23 acts on activated and memory T cells and promotes survival and expansion of the T cell subset, Th17. Th17 cells produce proinflammatory cytokines including IL-6, IL-17, TNFα, IL-22 and GM-CSF. IL-23 also acts on natural killer cells, dendritic cells and macrophages to induce pro-inflammatory cytokine expression. Unlike IL-23, IL-12 induces the differentiation of naïve CD4+ T cells into mature Th1 IFNγ-producing effector cells, and induces NK and cytotoxic T cell function by stimulating IFNγ production. Th1 cells driven by IL-12 were previously thought to be the pathogenic T cell subset in many autoimmune diseases, however, more recent animal studies in models of inflammatory bowel disease, psoriasis, inflammatory arthritis and multiple sclerosis, in which the individual contributions of IL-12 versus IL-23 were evaluated have firmly established that IL-23, not IL-12, is the key driver in autoimmune/inflammatory disease (Ahern et al., Immun. Rev. 2008 226:147-159; Cua et al., Nature 2003 421:744-748; Yago et al., Arthritis Res and Ther. 2007 9(5): R96). It is believed that IL-12 plays a critical role in the development of protective innate and adaptive immune responses to many intracellular pathogens and viruses and in tumor immune surveillance. See Kastelein, et al., Annual Review of Immunology, 2007, 25: 221-42; Liu, et al., Rheumatology, 2007, 46(8): 1266-73; Bowman et al., Current Opinion in Infectious Diseases, 2006 19:245-52; Fieschi and Casanova, Eur. J. Immunol. 2003 33:1461-4; Meeran et al., Mol. Cancer. Ther. 2006 5: 825-32; Langowski et al., Nature 2006 442: 461-5. As such, IL-23 specific inhibition (sparing IL-12 or the shared p40 subunit) should have a potentially superior safety profile compared to dual inhibition of IL-12 and IL-23.
Therefore, use of IL-23 specific antagonists that inhibit human IL-23 (such as antibodies that bind at least the unique p19 subunit or bind both the p19 and p40 subunits of IL-23) that spare IL-12 should provide efficacy equal to or greater than IL-12 antagonists or p40 antagonists without the potential risks associated with inhibition of IL-12. Murine, humanized and phage display antibodies selected for inhibition of recombinant IL-23 have been described; see for example U.S. Pat. No. 7,491,391, WIPO Publications WO1999/05280, WO2007/0244846, WO2007/027714, WO 2007/076524, WO2007/147019, WO2008/103473, WO 2008/103432, WO2009/043933 and WO2009/082624. However, there is a need for fully human therapeutic agents that are able to inhibit native human IL-23. Such therapeutics are highly specific for the target, particularly in vivo. Complete inhibition of the in vivo target can result in lower dose formulations, less frequent and/or more effective dosing which in turn results in reduced cost and increased efficiency. The present invention provides such IL-23 antagonists.